Journal
ASTRONOMY & ASTROPHYSICS
Volume 588, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201527728
Keywords
comets: individual: 67P/Churyumov-Gerasimenko; plasmas; magnetic fields; methods: data analysis
Categories
Funding
- German Ministerium fur Wirtschaft und Energie
- Deutsches Zentrum fur Luft- und Raumfahrt [50QP 1401]
- federal state of Bern
- Swiss National Science Foundation
- ESA PRODEX program
- CNRS
- CNES
- Observatoire de Paris and Universite Paul Sabatier
- Toulouse and Imperial College London
- UK Science and Technology Facilities Council
- STFC [ST/H002383/1, ST/K001051/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/H002383/1, ST/K001051/1] Funding Source: researchfish
- UK Space Agency [ST/K001698/1, ST/H004262/1, ST/P002250/1] Funding Source: researchfish
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Context. The Rosetta magnetometer RPC-MAG has been exploring the plasma environment of comet 67P/Churyumov-Gerasimenko since August 2014. The first months were dominated by low-frequency waves which evolved into more complex features. However, at the end of July 2015, close to perihelion, the magnetometer detected a region that did not contain any magnetic field at all. Aims. These signatures match the appearance of a diamagnetic cavity as was observed at comet 1P/Halley in 1986. The cavity here is more extended than previously predicted by models and features unusual magnetic field configurations, which need to be explained. Methods. The onboard magnetometer data were analyzed in detail and used to estimate the outgassing rate. A minimum variance analysis was used to determine boundary normals. Results. Our analysis of the data acquired by the Rosetta Plasma Consortium instrumentation confirms the existence of a diamagnetic cavity. The size is larger than predicted by simulations, however. One possible explanation are instabilities that are propagating along the cavity boundary and possibly a low magnetic pressure in the solar wind. This conclusion is supported by a change in sign of the Sun-pointing component of the magnetic field. Evidence also indicates that the cavity boundary is moving with variable velocities ranging from 230 500m/s.
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